1. Field of the Invention
The present invention relates to the use of a flexible crack spread preventing, separable web-type joining material in a method for joining a bearing face of a structure to a rigid covering layer to be provided thereon.
2. Description of the Prior Art
Due to thermal and mechanical movements in buildings and constructions, small cracks can develop in concrete structures with a size normally ranging from 0.1-0.5 mm. Under extreme conditions these cracks can have a width of even several mm.
Consequently, in building structures where a rigid covering layer, such as an ornamental layer of tile surface, is provided on a bearing face of a building, pool, stock container or bridge, there is a risk that on the occurrence of these cracks in said bearing face of, for example, concrete the covering layer will also crack.
As a result of these cracks considerable damage can be created due to among others;
leakage of (rain) water via the crack into a concrete construction causing corrosion in the armouring steel wire or in a steel bridge construction. PA1 leakage of water or e.g. chemical waste out of a stock container into the soil.
The European legislation at this moment requires for this reason that floors of warehouses, walls and floors of storage tanks etc. are protected against leakage. The German "Wasserhaushalts Gesetz" requires for such areas a crackbridging lining that is able to cover cracks of at least 0.2 mm.
At this moment various techniques are used to fullfill these requirements.
1. A thick lining made from highly flexible polymers such as flexibilised polyesters or polyurethanes. In general, the elongation at break for such products is over 100%. Due to the high flexibility, the mechanical and chemical properties of such linings are limited.
Such products have in general also a high plastic deformation next to the elastic deformation.
If a crack is formed underneath such linings the material, adjacent to the crack, will flow towards the crack and thus the crack remains covered. The crack bridging properties depend on the thickness of the lining and its flexibility which is strongly influenced by the temperature.
2. To overcome the limited mechanical and/or chemical properties of such linings, they can be covered by a nonwoven or woven reinforcement and protected by a covering layer with better mechanical and/or chemical properties. Such sandwich constructions combine the flexibility of the lower covering layer with the rigid properties of the top layer. Such constructions can generally cover cracks up till approximately 0.5 mm.
The problem is that they are very elaborative and difficult to apply--in particular on vertical surfaces.
The mechanical properties are limited since the brittle toplining can be pressed through the soft lower lining.
3. The third possibility is to make a rigid, e.g. glass reinforced lining like a tank in a tank. This lining is self supporting. In case of a crack in the substrate, the adhesion between the substrate and the lining is lost. Due to the selfsupporting character of the lining this is no problem as long as the delamination is limited. However due to frequent thermal expansions and contractions the delamination tends to grow and the lining can be completely loose its outer support. Besides, such linings are usually thick and expensive.
4. In order to eliminate the problems, it is also known to make use of, for example, elastified resin systems combined with a fibrous web.
When the bearing face cracks the elastified resin must then be capable of bridging the crack, but the crack-bridging action here depends on the quality which happens to exist in the adhesion to the bearing face. With good adhesion the crack-bridging action will generally be limited to less than 1 mm, depending on the thickness of the elastic covering layer and on the temperature. Only if the adhesion is poor good crack bridging can be obtained, since the fibrous web above the crack can only stretch with it if it is not adhering to the underlying bearing face.
Through the use of, for example, elastified polyester resins in these systems, one is, however, tied to a particular type of resin which limits the potential uses through its specific mechanical and chemical properties. There is also the problem that, due to high shrinkage, approximately 5%, and low alkali resistance, they can cause adhesion problems, as a result of which the covering can come away completely from the bearing face and loses its mechanical strength.
Such a known fixing of a bearing face with a rigid covering layer also produces many problems when one wishes to remove a fitted covering layer, since the known fixing is difficult to break.
Summarizing, in order to avoid damage to buildings and other constructions but also as a result of the increasing environmental concern, there is a growing interest in the use of protective and decorative lining systems with crackspread preventing properties.